Granular coated material



y 1, 1940. R. L. Maui-0N ET! AL 1,195

I GRANULAR COATED MATERIAL Filed Sept. 22. 1939 2 Shets-Sheet 1 INVENTORS. ROMIE Manon RAYMOND C. BENNEfi HENRY P K\RGHNER MW ATTORNEY.

May 21, 1940. R. MELTON m- AL GRANULAR COATED MATERIAL 2 Sheets-Sheet 2 Filed Sept. 22. 1939 Jay. 6.

INVENTOR-S ROMlE L. MELTON RAYMOND C. BENNER BY HENRY P. \RCHNER ATTORNEY.

Patented May 21,1940

' con'rnp newsman Romie L. Melton, Raymond C. Berliner, and Henry 1?. Kirchner, Niagara Falls, N. Y., assignors to The Carborundum Company, Niagara Falls, N. Y., a corporation of Delaware Application September 22, 1939, Serial No. 296,133

i Claims. (01. 51-185) This invention relates to the manufacture of granular coated webs of such material as paper, cloth and the like. More .particularly, this invention relates to the application of the sizing coat of adhesive to abrasive coated webs and the removal of such adhesive from the projecting points of the abrasive granules.

In the usual process, by which coated abrasive materials have been made for many years, it has been customary to coat the backing sheet of paper or cloth with a layer of glue or other suitable adhesive and then apply a layer of abrasive grains to the adhesively coated sheet. After this first layer of adhesive had set, a second or sizing l5 layer of adhesive was applied over the layer of abrasive grains in order to more firmly attach the grains to the Web backing. This sizing layer of adhesive was applied by means of a rubber covered roll partially immersed and revolving in a N pan of liquid adhesive and contacting with the abrasive coated surface. dried or set, the adhesive shrunk around the bases of the grains and held them firmly in position. 25 The quantity of adhesive applied by the glue roll was regulated by varying the pressure of the glue roll against the abrasive coated surface and pressure roll and thereby squeezing the layer-of adhesive to a desired thickness.

30 Thus the layer of sizing adhesive was applied as a sheet or blanket along on top of the' layer of abrasive granules. Due to the fluidity of the adhesive and the pressure from the rolls, the adhesive flowed down the sides of the grains and 35 partially filled the space between adjacent grains to more firmly anchor them to the base coating of adhesive. While this process was more effective in anchoring the abrasive granules securely in place it was disadvantageous in that the en- 40 tire surface of the abrasive grains remained covered with a film of adhesive and the sharp projecting points of the grains did not abrade' at their maximum efficiency. Furthermore the adhesive coated surface of the granules, which sof 5 tened by heat. retained particles of abraded material and quickly filled or clogged the spaces between the abrasive granules. This reduced the cutting efiiciency of the abrasive and materially reduced its effective life 50 The above difficulties were even more pronounced with the recently developed abrasive.

paper and cloth commonly known as oriented abrasive paper and cloth in which elongated granules of the abrasive grain have been oriented 55 with respect to the surface of the backing ma- When this sizing layer terial, so as to be upstanding therefrom and therefore in a position to afford a maximum cutting or abrading action.

We have found that the above difficulties of roll sizing can be overcome and the sizing ad- 5 hesive completely removed from the projecting tips of the abrasive grains by means of a jet or series ofjets arranged traversely across the web and adapted to direct a stream or series of streams of high velocity gas against the abrasive 10 coated surface. This gas issuitably heated and/or treated with a solvent of the adhesive so that it will not set or chill .the adhesive when directed against the grain tips but will drive the adhesive from the uppermost points of the grains down and around the bases of said grains. Thus the cutting points are freed of the deleterious effect of the adhesive film, a stronger bond is produced at the base of the grains and a greater space is provided'betweenthe grains for cutting clearance and the formation of chips during subsequent abrading action. i

A better understanding of'the invention may be obtained by reference to the accompanying drawings, in which: a Y

Figure 1 is an enlarged section through a fragment of the abrasive coated web at one stage of its manufacture;

Figure 2 is a similar section showing a fragment of an abrasive coated web in which the sizing adhesive has been applied in the usual way;

Figure 3 is a similar section showing a fragment of an abrasive coated web embodying our invention;

Figure 4 is a similar section showing a fragment of an abrasive coated web embodying an alternative form of our invention;

Figure 5 is a diagrammatic elevation of apparatus for manufacturing abrasive coated materials in accordance with our invention;

Figure 6 is a detailed side elevation of the adhesive applying mechanism shown diagram- -matically in Figure 5; and

Figure 7 is a front view of the apparatus shown in Figure 6.

Referring to Figure 3 which illustrates a fragment of an abrasive coated web made in accordance with our invention, the reference numeral 2 indicates the web or backing which may be of any of the usual flexible materials such as paper, cloth, vulcanized fiber or a combination of these or other suitable materials. Applied to one face ofthe web is a base coating 3 of adhesive, such as glue, varnish, silicate or synthetic resin. The particles of abrasive grain 4 are shown in oriented orupstanding position with respect to the backing and are so deposited onto the adhesive base coating 3 by suitable means not shown in the present application. The sizing layer of adhesive 5 is deposited principally around the base of the upstanding grains 4 filling the bottoms of the valleys and crevices between the adjacent grains.

It will be noted that the tops of the grains are free of the sizing adhesive and that the sharp.

projecting points are in condition for most efficient abrading. Furthermore the sizing adhesive applied to and built up around the bases of the elongated granules fills any depressions or irregularities in the surface of the individual grains and thereby increases the bonding or supporting action of the adhesive to hold the grains in position during subsequent use of the abrasive material.

Figure 1 shows a granular coated material prior to application of the sizing or reinforcing layer of adhesive. Only the bottoms of the granules 4 are in contact with the base layer of adhesive 3. This gives a very limited and insufficient support to the abrasive granules to maintain them against lateral pressure and grinding stresses when the coated web is used as an abradant.

It is necessary therefore to apply additional adhesive around the bases of the abrasive granules 4 so as to more firmly anchor them to the base coating and web backing material 2.

Figure 2 shows a granular coated web produced by the usual process, in which a blanket of adhesive 5a was applied over the granular coated surface and permitted to fiow down between the grains of its own accord. The tipsof the granular particles 4 are covered with a film of adhesive indicated by the reference 9. This film of adhesive is very detrimental when the coated material is used for abrasive purposes, since the tips of the grains are capped with the adhesive. ,In' addition to covering the sharp points of -the abrasive material, many adhesives soften during actual grinding, causing retention of abraded material and clogging of the spaces between the grains. This renders the abrasive material unfit for further use.

The preferred procedure in manufacturing granular coated webs in accordance with our invention will now be described. The previously coated abrasive material, such as that illustrated I by Figure 1, is moved from suitable drying racks (not shown) by means of the suction drum II, passed around the rubber-covered idler rolls l2, l3 and I4, and between the adhesive roll l5 and cooperating "pressure roll l6. The rubber-covered adhesive roll I5 is partially immersed and revolves in the liquid adhesive contained in the pan !'I so that a layer of sizing adhesive is applied to the abrasive side of the coated web. The pres sure roll I6 is adjustably supported above the adhesive roll and provided with adjusting means (see Figure 6) whereby the spacing between the rolls maybe varied and thereby regulate the quantity or thickness of the layer of adhesive applied to the abrasive side of the coated web.

After passing between the adhesive applying rolls l5 and I6, the coated web is moved past a jet of high velocity gas issuing from the adjustable orifice 3| of the air knife generally indicated by the reference numeral 30. This jet of high. velocity gas serves to drive the freshly applied layer of adhesive from the tips of the abrasive grains and cause it-to flow down and around the bases of the grains. I The coated web then passes over the suction drum 4!] and idler roll 4| to a suitable drying rack,

where it is formed in loops by the festooning device 42 and hung on the supporting bars 43 in a drying or curing chamber to fully set the adhesive. After drying or curing, the coated web is taken down from the rack and cut into pieces of various sizes and sold.

Referring now to Figures 6 and 7, the operation of the gas jet will be described in more detail. The adhesive pan I! is supported by a suitable frame 20, which also supports the adhesive roll l5 in such a manner thatsaid roll revolves in a liquid adhesive and applies a film or layer of said adhesive to the coated web I. The pressure roll 16 is also journaled on the frame 20 and adapted 'by a suitable bracket 24 and moves up or down with any vertical adjustment of the pressure roll 16. Thus the adjustment of the jet with respect to the surface of the coated web remains constant regardless of any vertical adjustment of the roll I6. However, the jet is adjustable with respect to the roll l6 and web I and means are provided for both angular and horizontal movement of the jet 3n. Cradle supports 25 are suitably mounted in gibs 26 secured to the bracket 24 and adapted to be moved horizontally by means of the small handwheel 21 and screw-threaded shaft 28 which are journaled on the bracket 24 and engage a threaded portion of the base of the said cradle 25. By loosening the clamping bolt 29, the jet 30 may be tilted by means of the handle 33 to any desired angle so that the impingement of the gas stream against the coated web can be at an angle of 90 thereto or at any desired oblique angle.

The thickness of the gas stream 3| issuing from the jet 30 may be adjusted by means of the bolts 32 which regulate the orifice opening of the jet 30. This orificeopening is readily adjustable from .002" to approximately .025" and may extend the full width of the web I, or, if desired, a number of such jets may be employed to cover the entire width of the web. It has been found that too thick a stream of gas causes splattering of the adhesive and does notcause the adhesive to flow down and around the bases of the grains as desired. Moreover, the impact of too thick a jet of high velocity gas will tend to blow over or entirely dislodge the upstanding granular particles on the coated web. We have found that a jet of approximately .005 inch in thickness is satisfactory for most purposes, though with drastic changes in size of granular particles, it may sometimes be necessary to increase or decrease the orifice opening. We have also found that the leading edge of the gas orifice should preferably be spaced from about /8 inch to of an inch from the tips of the granular particles carried by the coated web.

The gaseous medium employed is supplied to the jet 30 by means of a flexible hose connection 34, which connects to a suitable source of supply not shown. The internal construction of the jet 30 is such that the gas pressure is equal-- ized and the stream of gas issuing from the orifice is of uniform velocity throughout. The velocity of this gas stream appears to be of considerable magnitude, though it is difficult to express in actual units. We have found, however, that the required velocities may be obtained with a suitably designed jet at relatively low gas pressures ranging from 2 to 15 pounds per square inch gage and when an orifice opening of approximately .005 of an inch is employed, the gas velocity, and hence gage pressure, required will, of course, depend upon the character, condition and thickness of the particular adhesive being used. With thick viscous adhesives, a high gas pressure will be required, and with thin or less viscous adhesives, a relatively lower pressure will be required to clear such adhesive from the tips of the granular particles and produce a supporting mound of adhesive around the base of the granules. 7

We have found the character and composition of the gas stream to be of particular importance in carrying out the method of the present inven 'tion. Withadhesives that harden by evaporation of a solvent, we find it advisable to introduce a solvent of said adhesive into the gas to prevent setting of the adhesive before it is cleared away from the tips of the granules or built up around the bases thereof. When using thermoplastic adhesives, we may heat the gas sufliciently to prevent premature chilling and hardening of the adhesive, and with certain adhesives, we may add both a solvent and heat to the gas. Hide or animal glue, which falls in the latter classification, is the adhesive most generally used in the coatedabrasive industry and, for this reason, will be discussed in more detail. Such hide glue is applied to the coated Web at a temperature of approximately 150 F. and jells very quickly when the temperature drops much below F., or if there is any substantial evaporation of moisture. If the adhesive is permitted to become set or jelled, it cannot be properly removed from the tips or cutting points of the grains. For this reason it is necessary that the gas stream directed against the coated web be humidified with water vapor, which is a solvent for the glue, and heated to a temperature of F. or above. In actual practice we have found it convenient to use a mixture of heated compressed air and steam. The compressed air is heated to approximately 150 F. by means not shown, and sufiicient steam mixed therewith to saturate the air with water vapor. It is necessary that the compressed air and steam be thoroughly mixed, and for this reason, a separate mixing chamber (not shown in the drawings) is provided. We have found in certain instances that dry steam may be used alone as the gaseous medium, but for most purposes, it is desirable to use a mixture of com pressed air and steam.

Certain adhesives, such' as varnishes and synthetic resins of the alkyd, urea and phenol formaldehyde types, become softer and more liquid during the initial heating period. With these adhesives we prefer to use hot compressed air as the gaseous medium and to heat the air to a temperature of 100 F. to 300 F., depending upon the particular solvent employed in the adhesive used.

We have also found that the character of the coated abrasive material produced by the hereindescribed process-can be altered by varying the angle of impingement and velocity of the jet.

This jet of high velocity gas serves to drive the film of freshly applied adhesive from the tips of the abrasive grains and cause it to flow down and around the bases of the grains. The force of the jet produces a depression, indicated by the reference numeral 6 in Figure 3 of the drawings, in the adhesive film 5 between adjacent grains and forces the film of adhesive up along the sides of the grains, as indicated by reference 1, thereby surrounding the base of each individual granule in a mound of adhesive. When the angle of impingement of the jet is approximately 90 with respect to the surface of the coated web, the depression 6 of the adhesive film is approximately midway between adjacent grains, as shown in Figure 3. In an abrasive article of this character, the granules are supported against lateral displacement in an equal manner regardless of which direction the coated web is moved during subsequent grinding action.

By varying the angle of impingement of the gas stream so that it strikes the coated abrasive surface at an oblique angle, we are able to build up the mound of adhesive to a greater height on one side of the individual grains than on the other. This feature is clearly illustrated in Figure 4 of the drawings, in which the layer of sizing adhesive, generally indicated by 5, is shown as extending well up the back of the grains 4, as indicated by the reference "la. The depressed portion 6a of the adhesive film is well over near the front of the next succeeding grain. Thus a greater reinforcing or supporting action is ob-' tained by a given amount of sizing adhesive when the abrasive material is moved in the direction indicated by the arrow I 0. This feature is of particular importance in connection with abrasive belts used in grinding Wood, metals and other materials, and increases the rate of cut and effective life of the article to a marked degree. Grinding tests show an increase of as much as 25% in cutting rate and material abraded. Obviously, the abrasive belts must be driven in the proper direction in order to obtain maximum benefits from such a product. For this reason, the belts are suitably marked with an arrow to indicate the proper direction of movement.

The optimum angle of impingment of the gas jet depends upon the character of the abrasive coating desired and also upon the size, shape and position or degree of orientation of the grains with respect to the web backing. For this reason, we provide means for readily adjusting and maintaining the angle at which the jet of gas is directed at the surface of the adhesive sizing coating 5 on the web I. The jet may be adjustedthrough a wide arc, as indicated by the arrow 35 in Figures 5 and 6, by loosening the clamping bolt 29 and rotating the jet in the journals of the bracket 25. Such movement is facilitated by the handle 33, and when the angle is properly adjusted, the jet is securely locked in position by tightening the bolts 29. In producing coated abrasive material, such as that shown in Figure 4, we have found that satisfactory results are obtained when the angle of impingement of the gas stream is between 20 degrees and 75 degrees with respect to the surface of the coated web. More particularly, it has been found that the best resultsare obtained when the angle between the jet and the web is approximately 50 degrees.

Since the stream of gas strikes the coated web with appreciable force, we have found it 'sides of the granules to the bases thereof.

base coating of adhesive 3 before subjecting the abrasive coated web to the further treatment of a sizing coating of adhesive, as described in the present application. Such curing or setting of the base coating is efiected in a suitable curing zone through which the web is moved prior to passing over the drum II. This initial set or cure of the base coating prevents the upstanding abrasive granules 4 from being laid flat or entirely dislodged by the force of the gas stream. However, any loosely adhering or improperly attached granules are removed from the coated web.

. Other advantages in the herein-described process for applying the sizing layer of adhesive to abrasive coated articles will be apparent from a comparison of the sections of the coated webs illustrated by Figures 2, 3 and 4. The granular particles 4 are very irregular in shape and surface contour, particularly so with abrasive particles, so that a layer of sizing adhesive applied in the ordinary manner entraps air around the bases of a large portion of the grains. In Figure 2, which shows a section of granular material made by the usual process, reference numerals 8a, 8b, 8c and 8d indicate voids around the bases of the grains 4 which are not filled with adhesive. These voids are caused by the fact that a sheet or blanket of liquid adhesive is applied to the granular coated web in the usual process and the fluidity of the adhesive and pressure of the rolls are the only forces acting to cause the adhesive to fill the interstices between adjacent grains. Since the adhesive is fluid at the time. of application, it does tend to flow down the y crevices, however, are not properly filled because of the surface tension of the blanket of adhesive and the air entrapped in the said crevices. Obviously, these voids, such as 8a, materially weaken the anchorage of the granules and when the coated material is used as an abrasive, the rains are broken away from the backing before their useful life is spent.

In the granular coated material produced by the present process and illustrated by Figures 3 and 4, the above difficulties have been entirely eliminated. In addition to driving the film of adhesive from the tips of the granules, the force of the solvent treated gas stream is sufficient to fiow the adhesive into any crevices at the base of said grains and to displace any air which may have been entrapped therein.

While we have specifically illustrated and described the preferred embodiment of our invention, it is to be understood that the invention may be otherwiseembodied and practised within the scope of the following claims.

We claim:

1. As a new article of manufacture a granular coated web having granular particles adhesively attached to a web backing material and further supported by an additional layer of adhesive deposited around the bases of said particles and forming a supporting mound of adhesive located principally on one side of said granular particles.

2. As a new article of manufacture a granular coated web having granular particles adhesively attached to a web backing material and further supported by an additional layer of adhesive deposited around the bases of said particles and forming a supporting mound of adhesive located principally on one side of said granular particles,

the peaks of said granular particles being substantially devoid of said additional layer of adhesive.

3. As a new article of manufacture a granular coated web having granular particles adhesively attached to a web backing material and further supported by an additional layer of adhesive forming a mound around the bases of said particles and extending up the sides thereof, the peaks of said-granular particles being substantially free of said additional layer of adhesive.

4. As anew article of manufacture a granular coated web having granular particles adhesively attached to a web backing material and further supported by a mound of adhesive located principally on one side of said granular particles, the peaks of said granular particles being substantially devoid of said adhesive.

' ROMIE L. MELTON.

RAYMOND C. BENNER. HENRY P. KIRCH'NER. 

